This invention relates to data processing systems and more particularly to interconnection of a data processor and the keyboard of a peripheral device.
In a data processing system, the data that is processed is transferred into and out of the system through peripheral devices, such as magnetic tape or disc devices, card read or card punch devices, typewriters and control console. A typewriter, or a keyboard at the control console, is often used to manually enter data or instructions. The central processing unit (CPU) senses when a key has been depressed and takes appropriate action to interrupt the processing of data while a code identifying the key is read in.
A problem arises in properly identifying the key when the operator either depresses two keys in overlapping time or has so depressed one key that the key contacts bounce. It has been the practice of the industry to employ keyboards so designed as to eliminate the bounce problem, but the cost of such keyboards is significantly higher. The other problem, which may be referred to as a "key rollover" problem, could perhaps also be solved by a keyboard design having an interlock system which will not permit the second key contacts to make until the first key contacts break. However, such a solution of the rollover problem would make the cost of the keyboard too high for general use in low cost data processing systems. Therefore, it is an object of this invention to provide an improved key identifying system. Another object of the invention is to provide a key-bounce filtering system to eliminate double entry of a single key depressed once. Still another object is to provide a system for identifying in sequence two keys depressed in overlapping succession.